chore: bump version to 2.0.2

[stephenh-axiom-xyz]

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[github-actions]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

This PR is a mechanical version bump from v2.0.1 → v2.0.2 across Cargo.toml, Cargo.lock, docs, and scripts/download_setup.sh, with a matching CHANGELOG.md entry dated 2026-08-07. External stark-backend git dependencies are intentionally left at their own versions, which matches how they're managed in this workspace.

[github-actions]

group	app.proof_time_ms	app.cycles	leaf.proof_time_ms
fibonacci	(-14 [-0.9%]) 1,577	12,000,265	(+5 [+1.4%]) 364
keccak	(-62 [-0.7%]) 9,337	18,655,329	(+3 [+0.2%]) 1,534
sha2_bench	(-33 [-0.7%]) 4,966	14,793,960	(+3 [+0.5%]) 582
regex	661	4,137,067	(+1 [+0.5%]) 215
ecrecover	(+10 [+2.4%]) 434	123,583	(+1 [+0.5%]) 184
pairing	(+25 [+4.5%]) 578	1,745,757	(+1 [+0.5%]) 190
kitchen_sink	(-11 [-0.5%]) 2,222	2,579,903	(-4 [-0.8%]) 478

Note: cells_used metrics omitted because CUDA tracegen does not expose unpadded trace heights.

Commit: 483e1b9

Benchmark Workflow